1. Field of the Invention
The present invention relates to a heat generating element, in particular for an electric heating device of a motor vehicle, preferably with a positioning frame forming a holding fixture in which at least one PTC element is received, and two contact plates which are in contact with opposite sides of the PTC element.
2. Discussion of the Related Art
Such heat generating elements are generally known as a component of an electric heating device, in particular for heating air in a motor vehicle, which is also to be further developed with the present invention. The heat generating element forms a layer of a layered structure which commonly comprises corrugated fin elements that are in contact with both sides of the heat generating element. This layered structure commonly has at least a plurality of layers of corrugated fin elements and heat generating elements stacked in a plane.
A generic heat generating element is known from EP 2 190 256 A1. In this prior art, corrugated fins that are on the outside in contact with the heat generating element are adhesively bonded with the heat generating element. For this, curing insulating adhesive, such as silicone, is introduced into free spaces within the positioning frame and fills the remaining free spaces, so that the interior of the positioning frame is to be sealed hermetically by the insulating cured adhesive against the environment. The curing adhesive also reaches the phase boundary between the heat generating element and the corrugated fin elements, so that these corrugated fin elements are after curing of the adhesive connected to the heat generating element. The result is a self-contained heating rod that can as such be handled and placed or inserted into an electrical heating device.
The proposed solution according to EP 2 190 256 A1 has certain drawbacks. For example, heat expansion occurs during operation of the heat generating element. Due to the different nature of the components constituting the heat generating element, different thermal expansions arise. The cured insulating adhesive can not reliably compensate the different expansion values Permanent cracking occurs, so that the desired sealing effect by the cured adhesive for the heat generating element is lost.
Electrical heating devices comprising a heat generating element of the generic kind sometimes cause electromagnetic interference which are undesirable in particular in a motor vehicle as they are noticeable acoustically, for example, when operating a radio in the vehicle interior.